Exemplary embodiments of the invention relate to a differential gear for a motor vehicle.
U.S. Pat. No. 8,015,899 B2 discloses a differential gear for a motor vehicle, the differential gear comprises a housing part as a first gear part, as well as a crown wheel as a second gear part. The housing part and crown wheel are connected to each other via respective first connection surfaces running in the axial direction, by means of a press fit. Furthermore, the housing part and the crown wheel are connected to each other via respective second connection surfaces running at an angle to the axial direction, forming a welding seem that runs at an angle to the axial direction. This known differential gear has high production costs.
Exemplary embodiments of the present invention provide a differential gear that is more cost-efficient to produce.
To carry out a more cost-efficient production of the differential gear, it is provided in the first aspect of the invention, that one of the gear parts is formed from a steel and the other gear part from a cast iron material. In particular due to the use of the cast iron material, the material or production costs of the differential gear can be kept particularly low.
A further advantage of the differential gear according to the invention is that, due to the angled arrangement of the second connection surfaces, advantageous accessibility for a welding process is created, such that the gear parts can be welded to one other in a time-and cost-efficient manner. Due to the angled arrangement of the second connection surfaces, the welding process can also be moved or led at an angle to the axial direction, whereby collisions with one of the gear parts, in particular with the crown wheel, can be avoided in a simple manner.
A further advantage of the angled arrangement is that the welding seam can be checked by means of uninterrupted testing, in particular by means of ultrasound testing, in a simple and therefore cost-efficient manner. This is, in particular, advantageous compared to welding seams running in the axial direction, which are not able to be checked or only able to be checked at very high expense.
Furthermore, due to the angled arrangement of the second connection surfaces, and thus due to the angled arrangement of the welding seam, an at least fundamentally optimal load distribution can be achieved during the operation of the differential gear. Due to the angled arrangement of the second connection surfaces and thus the welding seam in combination with the press fit, at least fundamentally only pressure loads, in particular, compressive stresses, are transferred via the welding seam. Particularly in comparison to tensile loads, in particular tensile stresses, pressure loads only represent light loads for the welding seam, such that the differential gear also has high robustness and a high certainty of fulfilling its function.
A further aspect that keeps the production costs for the differential gear according to the invention low is that no screw connections are provided to connect the gear parts. The differential gear according to the invention can thus be produced with only a low material requirement, as no screw connections must be provided. Furthermore, this keeps the construction space requirement of the differential gear according to the invention low, whereby packaging problems can be solved and or avoided. The differential gear according to the invention is both applicable for a drive train of a commercial vehicle and of a passenger vehicle.
In an advantageous embodiment, the cast iron material is a grey cast iron. In other words, the other gear part is formed from the grey cast iron. This keeps the production costs of the differential gear according to the invention particularly low. Furthermore, the gear part formed from the grey cast iron has particularly advantageous mechanical properties.
In a particularly advantageous embodiment of the invention, the crown wheel is formed from the steel, in particular case-hardening steel, and the housing part from the cast iron material, in particular grey cast iron. The crown wheel thus has high robustness against high loads, such that particularly high torques can also be transferred onto the crown wheel. The housing part, which is less loaded compared to the crown wheel, is formed from the more cost-efficient cast iron material that has advantageous mechanical properties.
If the second connection surfaces connect directly to the first connection surfaces, then this is advantageous insofar as the crown wheel and the housing part (the gear parts) are produced with only a low material requirement and thus in a particularly cost-efficient manner. Furthermore, the differential gear has only a very low construction space requirement. In other words, in this embodiment, no spacing is provided between the first and second connection surfaces, for example via a respective, at least fundamentally radial wall. Rather, the first connection surfaces pass directly into the second connection surfaces.
For the depiction of a particularly cost-efficient production of the differential gear, it is advantageously provided that the welding seam, via which the gear parts are connected to one another, is formed as the welding seam known from German patent document DE 10 2008 027 167 A1. The gear parts therein are the mechanical components of the arrangement known from German patent document DE 10 2008 027 167 A1 of two mechanical components. During welding of the gear parts, a specific structure in the welding seam is inserted in a targeted manner. The welding of the gear parts can therein occur without the use of additional welding material. This keeps the production costs of the differential gear according to the invention particularly low.
Alternatively, it can be provided that a welding filler material with a proportion of nickel is used during welding of the gear parts. Thus, in particular, a particularly cheap metallurgic connection can be implemented between the gear parts.
The gear parts of the differential gear according to the invention are preferably welded to one another by means of a laser welding method. Thus, the gear parts can be connected to one another in a particularly time and cost-efficient manner, which keeps the production costs of the entire differential gear at a particularly low level.
In the second aspect of the invention, the second connection surfaces are connected directly to the first connection surfaces. In other words, the second connection surfaces, running at an angle, pass directly into the first connection surfaces running in the axial direction, or vice versa. The connection surfaces are thus not at a distance from one another, such that the differential gear can be produced with only a very low material requirement and has only a very low weight as well as a low construction space requirement. Advantageous embodiments of the first aspect of the invention are to be considered as advantageous embodiments of the second aspect of the invention and vice versa.
In a further advantageous embodiment of the invention, at least one further housing part is provided as a third gear part. The further housing part is, therein, connected to the first housing part via respective third connection surfaces running in the axial direction, by means of a press fit, and via respective fourth connection surfaces running at an angle to the axial direction, forming a further welding seam.
As has already been described for the second connection surfaces, the angled arrangement of the fourth connection surfaces have the advantage of particularly simple accessibility for production of the welding seam, such that the gear parts are to be connected to one another in a time and cost-efficient manner. Furthermore, the further welding seam can be checked in a simple manner by means of uninterrupted testing, for example for inclusions or similar malformations.
The combination of the further welding seam with the further press fit has the advantage that only pressure loads are transferred via the further welding seam, such that the differential gear has a high certainty of fulfilling its function and a long life span.
The differential gear according to the invention also enables the advantageous and cost-efficient representation of a modular system. Such a modular system comprises a plurality of crown wheels that are differentiated from one another as first gear parts, a plurality of first housing parts that are differentiated from one another as second gear parts and, if necessary, a plurality of further housing parts that are differentiated from one another as third gear parts. Due to the corresponding, advantageous connections of the gear parts to one another via the press fits and the welding seams, a respective differential can be produced from the respective gear parts in a time and cost-efficient manner. Thus, the modular system enables a production of various differentials according to need, which are adapted to respective use purposes, for example to use in a road vehicle, in a construction vehicle or similar.
In a further advantageous embodiment, the further housing part is formed from steel. Thus, it can withstand high operation demands.
For the implementation of only a low construction space requirement, the fourth connection surfaces are connected directly to the third connection surfaces. The further housing part and the first housing part can thus also be produced with only a very low material requirement and thus cost-efficiently.
In a further advantageous embodiment, the fourth connection surfaces enclose an angle with the axial direction in a range of 25° to 65° inclusive. Advantageously, the fourth connection surfaces enclose an angle with the axial direction of at least fundamentally 60°. Thus, a particularly advantageous accessibility to the fourth connection surfaces is created, such that the first housing part and the further housing part can be connected to each other in a time and cost-efficient manner.
In a further embodiment of the invention, the second connection surfaces enclose an angle with the axial direction in a range of 25° to 65° inclusive. Preferably, the angle between the second connection surfaces and the axial direction amounts to at least fundamentally 60°. Thus, as a consequence thereof, there is very good accessibility to the second connection surfaces, such that the crown wheel can be connected to the first housing part in a time and cost-efficient manner.
Further advantages, features and details of the invention result from the description below of preferred exemplary embodiments, as well as by means of the drawing. The features and combinations of features named above in the description as well as the features and combinations of features named in the description of figures and/or shown solely in the figures are not only applicable in the respective specified combinations, but also in other combinations or stand-alone, without leaving the scope of the invention.